The invention relates to control systems for hydrostatic transmissions for propulsion of vehicles and more particularly, to electronic means for maintaining a desired path or track of operation without operator intervention.
There are many circumstances under which it is highly desirable to have a hydrostatic transmission driven vehicle, such as a crawler tractor, operate in a straight line or in a predefined curve without driver intervention. For example, in farming or in various types of construction work, it is considered desirable to have a track vehicle maintain a straight path of travel with less than one foot of deviation in each 100 feet of forward or rearward movement. Predetermined paths of operation should be obtainable where the operator merely selects the speed and direction (forward or reverse) by operating a single speed and direction control lever.
However, in practice it has been found that in some types of hydrostatic transmissions, fluid leakages and slightly mismatched hydraulic components result in one track turning at a slightly higher velocity than the other. A number of hydraulic solutions to this problem have been proposed as illustrated in the U.S. Pat. Nos. to Burton, 3,789,940; Long, 3,543,654; and Lauck et al., 3,812,925. A hydraulic solution, however, calls for the use of relatively expensive and bulky hyraulic components which also require close tolerances for effective operation.